In the environment of automated controlled processes and industrial networks there are high requirements concerning real-time capability of the communication between the individual network and communication subscribers (briefly referred to as subscribers below), regardless of whether the respective communication system is based on conventional fieldbus technologies or industrial Ethernet technologies. A key aspect to meet the real-time requirements is to ensure precisely timed cyclic communication. For example, first each subscriber gets assigned a time slot during which it is allowed to transfer a limited amount of data. Second, each communication cycle is divided into time periods for transmission of real-time data and time periods for transmission of non-real-time data, in order to prevent the two data categories from mutual influence. Another crucial aspect is precise time synchronization of the communication subscribers. For this purpose, special protocols such as the “Simple Network Transport Protocol” (SNTP, according to RFC4330) or the “Precision Time Protocol” (PTP, according to IEEE1588) may be employed, which are intended for time synchronization of clocks distributed in the network. Another protocol for time synchronization that can be mentioned is the “Precision Transparent Clock Protocol” (PTCP, according to IEC61158) which is for example employed in PROFINET-based communication systems.
According to PTCP, the clocks of the subscribers are organized in a master-slave hierarchy, and synchronization of the clocks is accomplished by exchanging different PTCP telegrams. For this purpose, four types of telegrams are defined according to PTCP, which require a highly accurate determination of the transmission times of the respective telegrams. These PTCP telegrams are generated by four different PTCP modules or state machines implemented in the application layer. Specifically, these include synchronization telegrams of the PTCP master protocol machine or the PTCP slave protocol machine and request telegrams of the line delay request protocol machine and response telegrams of the line delay response protocol machine. These telegrams are generated by the PTCP modules independently of each other and asynchronously to each other, and therefore they might be provided at the same time for being transmitted. In the case of the synchronization telegrams of the PTCP master protocol machine and of the PTCP slave protocol machine, the ascertained transmission times are directly written into and transmitted with the telegram. In the case of the request telegrams of the line delay request protocol machine and the response telegrams of the line delay response protocol machine, however, the ascertained transmission times are read out to be sent only with a subsequent telegram.
Hitherto, special hardware was necessary for transmitting such telegrams and for most precisely ascertaining and associating the transmission times. Network controllers for use in industrial networks that have a sufficiently precise time stamp unit implemented in hardware are available, for example, under the product names “ERTEC” of Siemens, “NETX” of Hilscher, or “TPS-1” of Renesas/Phoenix Contact. However, such special network controllers are very expensive, especially when compared to conventional network controllers known in the PC sector, which are intended for use in private networks or office networks.
However, for some time network controllers have been available, which are made from inexpensive standard components known in the PC sector and should allegedly still be suitable for use in industrial networks. For example, such a network controller with the product name “I210” has been available from Intel since the end of 2012.